chore: Archive 7 unused workflows and consolidate to SSOT pipeline

Reorganized .gitea/workflows/ to reduce duplication and noise:
- Archived 7 unnecessary workflows to .archived/ subdirectory:
  - auto_backup_schedule.yml
  - backup.yml
  - calibration_backlog.yml
  - kis_data_collection.yml
  - qualitative_sell_strategy.yml
  - snapshot_admin.yml
  - wbs_9_3_null_policy_ci_gate.yml

Active workflows (5 total):
- merge-to-main.yml (SSOT 5-stage pipeline)
- ci.yml (PR validation)
- deploy-prod.yml (manual deployment)
- fast-validation.yml (PR fast checks)
- _common/build-and-test.yml (reusable component)

Rationale: Phase 2 deployment infrastructure is complete. Legacy workflows
are no longer needed, reducing CI/CD maintenance burden and improving clarity.
Archived workflows remain available for reference if rollback is needed.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

.gitea/workflows/.archived/backup.yml

@@ -0,0 +1,15 @@
+name: backup
+
+on:
+  schedule:
+    - cron: "0 0 * * *"
+  workflow_dispatch: {}
+
+jobs:
+  backup:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Run backup
+        run: python tools/backup_data_feed_and_databases_v1.py
+